Fluid pump noise reduction means

ABSTRACT

A rotary vane air pump for the exhaust system of an internal combustion engine has an air inlet modified for quieter operation by the extension of the air inlet passage and the addition, at the junction of the extended inlet passage and the pump working chamber, of an accumulator volume open to the inlet passage and working chamber but outside the main flow of air through the pump.

Umted States Patent 1191 1111 3,844,696

Stiles et al. Oct. 29, 1974 [54] FLUID PUMP NOISE REDUCTION MEANS 3,370,785 2/1968 Pa seket al 418/137 X [75] Inventor Jo L. Stiles Sag n Herbert E- 3,459,275 8/1969 Prlllwltz et al 418/181 X Z'hLB'd t,b th fM' h. Ie n gepor o lc Primary Examiner-C. J. Husar Asslgneei P Corporation, Assistant Examiner-Leonard Smith Dem)", Mlch- Attorney, Agent, or Firm-Robert M. Sigler [22] Filed: Aug. 21, 1973 [21] Appl. No.2 390,307 ABSTRACT A rotary vane air pump for the exhaust system of an 52 US. Cl. 418/181, 418/137 internal combustion engine has an air inlet modified [51] Int. Cl. F04c 29/06 for quieter operation by the extension of the air inlet [58] Field of Search 418/138, 181, 241; Passage and the addition, at the junction of the 417/312 181/35 A, 36 R, 36 D tended inlet passage and the pump working chamber, of an accumulator volume open to the inlet passage [56] References Cited and working chamber but outside the main flow of air UNITED STATES PATENTS thmugh the Pump- 3,270,955 9/1966 Huyser et al 418/181 X 2 Claims, 6 Drawing Figures 5 1- 6 l w w a4 r8 i 2 BACKGROUND OF THE INVENTION Injection of air into the stream of hot exhaust gases emitted from the combustion chambers of an internal combustion engine is a well known method of reducing the proportion of unburned and partially burned hydrocarbons in such exhaust gases. It has been found that a semi-articulated rotary vane pump is a very efficient and economical type of pump for supplying air at the required pressure and rate for such an application. A good example of such a pump with two vanes is shown in US. Pat. No. 3,370,785, issued Feb. 27, 1968 to J. E. Pasek et al. A similar pump with three vanes provides greater pump capacity.

Even a rotary pump, however, is subject to the problem of noise generated by the rhythmically changing air pressure in the pump working chamber and air inlet. Such noise can be .objectionable to vehicle occupants, particularly at low speeds where it is not masked by other engine, road or wind noises.

One obvious method of suppressing this noise would be to mount a separate silencer on the pump inlet. However, it would be difficult to fix a silencer to a pump such as that shown in the aforementioned Pasek patent because of its centrifugal inlet air filter; and any separate silencer that could be designed for such a pump would be quite expensive.

It would therefore be desirable to suppress pump generated noise within the pump itself. Analysis of the pump generated noise shows it to consist of a composite of frequencies, the lowest of which, known as the fundamental frequency, is the frequency at which the pump vanes pass the pump inlet. The remaining frequencies are all higher harmonics of the fundamental frequency; that is, integral multiples of the fundamental frequency and frequencies which are the sum or difference of other harmonics. Ordinarily, the fundamental frequency and the lowest integral multiples thereof dominate the composite; all other harmonics are therefore negligible. The relative dominance of the fundamental and lowest harmonics is generally determined by the natural resonant frequency of the pump inlet, which is a specific result of pump design. The relative energies of ascending harmonics generally show a gradual decline from that harmonic nearest the natural frequency of the pump inlet. It has been found that adding an accumulator or ballast volume to the inlet of the pump working chamber will tend to decrease the natural frequency of the pump inlet and that simultaneously extending the inlet passage through which air flows to the pump working chamber and accumulator volume tends to produce a steeper decrease in the relative energy of harmonics above the natural frequency of the pump inlet. Therefore, if the natural frequency of the pump inlet were to be reduced below the pumps fundamental frequency and the pump inlet passage were sufficiently extended, the harmonics would be significantly reduced in energy.

With such a pump mounted on an engine in a vehicle under normal driving conditions, pump noise above 3,000 RPM engine speed is masked by other noise from the engine, road or wind and can therefore be ignored. Below 3,000 RPM engine speed, with a three vane pump driven at engine speed, the fundamental pump frequency is 150 Hz or lower; and at 1,000 RPM engine speed, slightly above idle speed for most vehicles, the fundamental pump frequency is only 50 Hz. Noise at such low frequencies would not be as apparent to the occupants of the vehicle as would be the noise of the higher harmonics which are reduced.

SUMMARY OF THE INVENTION It is therefore the object of this invention to provide a semi-articulated rotary vane pump having a working chamber with an inlet thereto, .an extended inlet passage for the conduction of air into said working chamber inlet and an accumulator volume open to said working chamber inlet but outside the normal flow path of fluid through the pump.

The extended inlet passage is to be accomplished while maintaining the compact pump size by adding a shroud to form a shroud volume between the axial end of the pump body and the centrifugal filter, an axially extending passage outside the pump body from the shroud volume to the opposite axial end of the pump and a circumferentially extending passage outside the pump body from the other end of the axially extending passage to the pump working chamber inlet.

The accumulator volume is formed by increasing to a maximum extend the volume of the pump working chamber inlet not swept by the vanes and providing for the introduction of air into said pump working chamber inlet at the far end of said inlet in the direction of vane rotation.

Further details and objects of this invention will be apparent in the following detailed description of the drawings and preferred embodiment.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a cutaway elevational view of the pump according to the invention.

FIG. 2 is a section view along line 2--2 in FIG. 1.

FIG. 3 is a section view along line 3-3 in FIG. 1.

FIG. 4 is a section view along line 4-4 in FIG. 3.

FIG. 5 is a section view along line 55 in FIG. 1.

FIG. 6 shows the pump of FIGS. 1 5 in its environment.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 6, an internal combustion engine 2 has an exhaust manifold 4 for the conduction of hot exhaust gases from its cylinders. An air pump 6 mounted on the engine 2 is driven by the engine through belt 8 and pulley 9 to supply air to the exhaust manifold 4 through an air supply conduit 10. The air so supplied to the hot exhaust gases is helpful in reducing the proportion of unburned and partially burned hydrocarbons in said exhaust gases.

The air pump 6 is shown in detail in FIGS. 1 5. Referring to FIG. 1, a concave housing 14 is closed by a cover plate 16. As shown in FIG. 5, the interior wall 18 of housing 14 is of circular cross section. A rotor 20 disposed in housing 14 on an axis eccentric to the axis of the housing has an exterior wall 22 which is tangent to the internal wall 18 of housing 14 at its lowest point to provide stripping land 24.

The internal wall 18 is recessed on opposite sides of the stripping land 24 to form an outlet chamber 26 and an inlet chamber 28. A shaft 30 is fixed in cover plate 16 and extends into housing 14 concentrically with the internal wall 18. Three pairs of bearing supported counterweight hubs 32 are positioned on shaft 30. Around each pair of hubs 32 is molded a vane 34 which locks into the hubs 32 as shown in FIG. 5. Each vane 34 extends out toward the internal wall 18 of the housing 14.

Rotor 20 surrounds shaft 30 and hubs 32 and is provided with slots 36 through which vanes 34 extend. As shown in FIG. 1, rotor 20 has an integral shaft 38 extending through an end wall 40 of housing 14. A hub 42 is pressed onto shaft 38 and the pulley 9, shown in FIG. 6, is bolted to the hub 42 for engagement with belt 8 so that the shaft 38 and rotor 20 are driven by the engine 2. The rotor 20 and vanes 34 form an impeller, the vanes of which are forced to rotate with the rotor 20 and thus sweep through a crescent-shaped working chamber 44 (counterclockwise as viewed in FIG. to draw air from inlet chamber 28 and direct a pressurized stream of air into outlet chamber 26. Stripping land 24 prevents leakage of air between outlet chamber 26 and inlet chamber 28.

As shown in FIG. 5, the internal wall 18 of housing 14 is provided with notches 46 between the working chamber 44 and the outlet and inlet chambers 26 and 28. Notches 46 reduce sudden pressure changes as vanes 34 pass the inlet and outlet chambers 28 and 26 and so contribute to smooth and quiet operation of the pump.

As shown in FIG. I, end wall 40 of housing 14 and cover plate 16 are provided with interior recesses 48 and 50 into which the ends of rotor extend. Shoulders 52 and 54 in the recesses 48 and 50 seal the exterior wall 22 of the rotor 20 to close the ends of the working chamber 44. As shown most particularly in FIG. 5, metal liners 56 spotwelded within the rotor 20 form recesses 58 provided with slots 60 through which the vanes 34 project. The recesses 58 hold sealing shoe strips 61 biased against each side of the vanes 34 to seal the working chamber 44 from the interior of the rotor 20.

Referring again to FIG. I, an annular cap 62 is pressed inside the open end of the rotor 20. The annular cap 62 forms a bearing mounting surface for a roller bearing 64 which supports this end of the rotor 20 on a cylindrical inner hub portion 66 of the cover plate 16.

A shaft 38 at the other end of the rotor 20 has pressed thereon a ball bearing 68, which is supported by an injected and hardened annular plastic ring 70 within a circular opening 72 in the end wall 40 of the housing I4.

On the outside of the end wall 40 is pressed a shroud 74, consisting of a circular disc 75 with a peripheral flange 76 and radial wing 77 as shown in FIG. 2. The shroud 74 is preferably molded of a glass reinforced plastic. A shroud volume 78 is formed between the shroud 74 and the end wall 40.

A centrifugal air cleaner 80 having a plurality of radially extending passages 81 is pressed on the hub 42 adjacent the shroud 74. An inward axially extending flange 83 on the centrifugal air cleaner 80 makes sliding contact with the peripheral flange 76 of the shroud 74 to enclose an air collection volume 82 between said air cleaner 80 and shroud 74. Each radially extending passage 81 is open to the atmosphere at its outer radial end and to the air collection volume 82 through an axially directed aperture 84. Centrifugal air cleaner 80 allows air to be drawn therethrough into the air collection volume 82 but'spins out contaminating particles by centrifugal force.

Referring to FIG. 2, an opening 85 through the disc of the shroud 74 near the peripheral flange 76 thereof allows the air in the air collection volume 82 to pass into the shroud volume 78. As shown in FIGS. 2 and 5, which are section views from opposite axial directions, the opening 85 is axially aligned with the inlet chamber 28.

Referring to FIG. 5, an external peripheral wall 86 of the housing 14 forms, with the cover plate 16, a circumferential passage 88 around the top of the pump. As shown in FIG. 1, the circumferential passage 88 is located adjacent the axial end of the pump opposite that which includes the shroud 74. At one end, on the right side in FIG. 5, the external peripheral wall 86 merges with the internal peripheral wall 18 where it has expanded outwardly to form the inlet chamber 28. At this end, the circumferential passage 88 is open to the inlet chamber 28 through an opening 89 adjacent the notch 46.

At its other end, diametrically opposite the inlet chamber 28, the external peripheral wall 86 merges into an external axial wall 90, which forms an axial passage 91 which is open to the circumferential passage 88 at this end. As can be seen most clearly in FIG. 4, the external axial wall 90 extends to the opposite axial end of the pump, where it meets the radial wing 77 of the shroud 74. A recessed notch 92 at the junction of the end wall 40 and internal wall 18 allows the axial passage 91 to communicate with the shroud volume 78 at a point diametrically opposite the opening 85.

Thus an extended inlet passage for the pump has been established. Air from the atmosphere enters through the centrifugal filter into the air collection volume 82. From there it must pass through the opening into the shroud volume 78 and flow across to the diametrically opposite side of the shroud volume 78, where it can passinto the axial passage 91. The air follows the axial passage 91 to the opposite axial end of the pump, where it enters the circumferential passage 88. The air then follows the circumferential passage 88 peripherally around the pump and through the opening 89 into the inlet chamber 28.

Referring to FIG. 5, it should be noticed that, due to the offset axes of the vanes 34 and rotor 20, the vanes 34 are contained within the rotor 20 as they pass the stripping land 24 and gradually emerge from the rotor 20 as they rotate until they close off the working cham ber 44 just past the notch 46 by the opening 89. It should also be apparent that the opening 89 is placed as far as possible toward the end of the inlet chamber 28 in the direction of vane and rotor rotation. This results in a large portion of the inlet chamber 28 which is not swept by the vanes 34 and is outside the main stream of air which flows around the circumferential passage 88, through the opening 89 and through the working chamber 44 in a counterclockwise direction. This volume is designated the accumulator volume 94. The air within the accumulator volume 94 serves as an air ballast to smooth out sudden pressure changes caused by the vanes 34 moving past the opening 89 and through the working chamber 44. The accumulator volume 94 as shown is large enough to reduce the natural resonant frequency of the pump to a level near or below the fundamental frequency at which the vanes enter the working chamber 44. This lowered natural frequency plus the suppression of higher harmonics by the extended inlet passage provides a pump the emitted noise of which is less discernible to the occupants of a vehicle on which the pump is used.

The pump described above is a preferred embodiment of our invention, and other embodiments will occur to those skilled in the art. Therefore, our invention is to be limited only by the claims which follow.

We claim:

1. A positive displacement air pump for use in a system for supplying air to the stream of hot exhaust gases emitted from a combustion engine; said pump including a generally cylindrical housing, a working chamber inside said housing having an inlet and an outlet; an impeller in said working chamber for directing an air stream through said working chamber from said inlet to said outlet and increasing the pressure in said air stream and a shroud fixed to one axial end of said housing, said shroud having a portion thereof spaced from said housing to form a shroud volume and having a hole therethrough; said housing including a passage extending circumferentially around said working chamber adjacent the other axial end of said housing, said circumferential passage having one end open to said inlet and another end diametrically opposite said inlet; said housing also including a passage extending axially outside said working chamber, said axial passage communicating said other end of said circumferential passage with said shroud volume; said shroud opening, shroud volume, axial passage, circumferential passage and inlet forming an extended inductive inlet passage for said working chamber; said housing further including an accumulator volume in communication with said working chamber and said extended inductive inlet passage; said extended inductive inlet passage and said accumulator volume combining to reduce the noise emitted by said pump.

2. An air pump adapted for use in a system for supplying air to the stream of hot exhaust gases emitted from a combustion engine, said air pump including a housing having axially spaced end walls connected by a horizontally extending cylindrical internal peripheral 6 wall forming a cavity, an impeller positioned within said cavity having a cylindrical rotor radially spaced from portions of said internal wall to form a crescentshaped working chamber and a plurality of axially extending radial vanes adapted to rotate with said rotor about a parallel offset axis, said housing internal wall having an axially extending portion tangent to the lowermost portion of said rotor and forming a stripping land, said internal wall having a pair of recesses adjacent and on opposite sides of said stripping land forming inlet and outlet volumes for said working chamber, said rotor and vanes being adapted upon rotation to direct an air stream through said working chamber from said inlet volume to said outlet volume and to increase the pressure in said air stream; said air pump further including a shroud fixed to one axial end thereof, said shroud having a portion thereof spaced from one axial end wall to form a shroud volume and having an opening therethrough axially aligned with said inlet volume, said air pump further including wall means outside said internal peripheral wall defining a passage extending circumferentially around said internal peripheral wall adjacent the other axial end of said air pump and having one end thereof open to said inlet volume at the circumferential end of said inlet volume opposite said stripping land and another end thereof diametrically opposite said inlet volume said air pump including further wall means outside said internal peripheral wall defining a passage extending axially between said other end of said circumferential passage and said shroud volume diametrically opposite said shroud opening; said shroud opening, shroud volume, axial passage, circumferential passage and inlet volume comprising an extended inductive inlet passage for said pump; said inlet volume including an accumulator volume which is not swept by said vanes and extends peripherally around said rotor from the opening of said circumferential passage to said stripping land, said extended inductive inlet passage and said accumulator volume combining to reduce the noise emitted by said pump. l 

1. A positive displacement air pump for use in a system for supplying air to the stream of hot exhaust gases emitted from a combustion engine; said pump including a generally cylindrical housing, a working chamber inside said housing having an inlet and an outlet; an impeller in said working chamber for directing an air stream through said working chamber from said inlet to said outlet and increasing the pressure in said air stream and a shroud fixed to one axial end of said housing, said shroud having a portion thereof spaced from said housing to form a shroud volume and having a hole therethrough; said housing including a passage extending circumferentially around said working chamber adjacent the other axial end of said housing, said circumferential passage having one end open to said inlet and another end diametrically opposite said inlet; said housing also including a passage extending axially outside said working chamber, said axial passage communicating said other end of said circumferential passage with said shroud volume; said shroud opening, shroud volume, axial passage, circumferential passage and inlet forming an extended inductive inlet passage for said working chamber; said housing further including an accumulator volume in communication with said working chamber and said extended inductivE inlet passage; said extended inductive inlet passage and said accumulator volume combining to reduce the noise emitted by said pump.
 2. An air pump adapted for use in a system for supplying air to the stream of hot exhaust gases emitted from a combustion engine, said air pump including a housing having axially spaced end walls connected by a horizontally extending cylindrical internal peripheral wall forming a cavity, an impeller positioned within said cavity having a cylindrical rotor radially spaced from portions of said internal wall to form a crescent-shaped working chamber and a plurality of axially extending radial vanes adapted to rotate with said rotor about a parallel offset axis, said housing internal wall having an axially extending portion tangent to the lowermost portion of said rotor and forming a stripping land, said internal wall having a pair of recesses adjacent and on opposite sides of said stripping land forming inlet and outlet volumes for said working chamber, said rotor and vanes being adapted upon rotation to direct an air stream through said working chamber from said inlet volume to said outlet volume and to increase the pressure in said air stream; said air pump further including a shroud fixed to one axial end thereof, said shroud having a portion thereof spaced from one axial end wall to form a shroud volume and having an opening therethrough axially aligned with said inlet volume, said air pump further including wall means outside said internal peripheral wall defining a passage extending circumferentially around said internal peripheral wall adjacent the other axial end of said air pump and having one end thereof open to said inlet volume at the circumferential end of said inlet volume opposite said stripping land and another end thereof diametrically opposite said inlet volume said air pump including further wall means outside said internal peripheral wall defining a passage extending axially between said other end of said circumferential passage and said shroud volume diametrically opposite said shroud opening; said shroud opening, shroud volume, axial passage, circumferential passage and inlet volume comprising an extended inductive inlet passage for said pump; said inlet volume including an accumulator volume which is not swept by said vanes and extends peripherally around said rotor from the opening of said circumferential passage to said stripping land, said extended inductive inlet passage and said accumulator volume combining to reduce the noise emitted by said pump. 